The present invention generally relates to an implantable device for applying cardioverting electrical energy to at least one chamber of a patient's heart in need of cardioversion and a warning to the patient indicating the imminent delivery of the cardioverting energy. The present invention is more particularly directed to a fully automatic implantable atrial defibrillator which exhibits improved safety by providing warning electrical energy to the patient when the patient's heart is in need of cardioversion and at least a predetermined time before the delivery of cardioverting electrical energy to the atria of the patient's heart. The warning electrical energy is of a quantity which is less discomforting than the quantity required to cardiovert the atria. More specifically, the warning electrical energy is of sufficient quantity so as to be readily discernable by the patient but of insufficient quantity to intentionally cardiovert the atria of the heart.
Atrial fibrillation is probably the most common cardiac arrhythmia. Although it is not usually a life threatening arrhythmia, it is associated with strokes thought to be caused by blood clots forming in areas of stagnant blood flow as a result of prolonged atrial fibrillation. In addition, patients afflicted with atrial fibrillation generally experience palpitations of the heart and may even experience dizziness or even loss of consciousness.
Atrial fibrillation occurs suddenly and many times can only be corrected by a discharge of electrical energy to the heart through the skin of the patient by way of an external defibrillator of the type well known in the art. This treatment is commonly referred to as synchronized cardioversion and, as its name implies, involves applying electrical defibrillating energy to the heart in synchronism with a detected ventricular electrical activation (R wave) of the heart. The treatment is very painful and, unfortunately, most often only results in temporary relief for patients, lasting but a few weeks.
Drugs are available for reducing the incidence of atrial fibrillation. However, these drugs have many side effects and many patients are resistent to them which greatly reduces their therapeutic effect.
Implantable atrial defibrillators have been proposed to provide patients suffering from occurrences of atrial fibrillation with relief. Unfortunately, to the detriment of such patients, none of these atrial defibrillators have become a commercial reality.
Two such proposed defibrillators, although represented as being implantable, were not fully automatic, requiring human interaction for cardioverting or defibrillating the heart. Both of these proposed defibrillators require the patient to recognize the symptoms of atrial fibrillation with one defibrillator requiring a visit to a physician to activate the defibrillator and the other defibrillator requiring the patient to activate the defibrillator with an external magnet.
Improved implantable atrial defibrillators and lead systems which exhibit automatic operation are fully described in copending U.S. applications, Ser. No. 07/685,130, filed Apr. 12, 1991, in the names of John M. Adams and Clifton A. Alferness for IMPROVED ATRIAL DEFIBRILLATOR AND METHOD and Ser. No. 07/856,514, filed Mar. 24, 1992, in the names of John M. Adams, Clifton A. Alferness, and Paul E. Kreyenhagen for IMPROVED ATRIAL DEFIBRILLATOR, LEAD SYSTEMS, AND METHOD, which applications are assigned to the assignee of the present invention and incorporated herein by reference. The atrial defibrillator disclosed in the aforementioned referenced applications, are truly automatic by including an atrial fibrillation detector which, responsive to sensed atrial activity, determines when the atria of the heart are in need of cardioversion. When the atrial fibrillation detector determines that the atria are in fibrillation and thus in need of cardioversion, the atrial fibrillation detector causes a cardioverter stage to deliver defibrillating or cardioverting electrical energy to the atria in timed relation to a detected ventricular electrical activation (R wave) of the heart. As a result, the atria are automatically and safely cardioverted.
Unfortunately, the quantity of electrical energy which is required to cardiovert or defibrillate the atria is sufficient, in most cases, to cause a sudden pain in the patient's chest area or stun the patient. In addition, the successful cardioversion or defibrillation of the atria may also result in a rapid decrease in the patient's heart rate from a high and possibly variable heart rate. This rapid change in heart rate can, for some patients, cause discomfort or even temporary dizziness. As a result, it would be highly desirable to provide a warning to a patient prior to the delivery of cardioverting or defibrillating electrical energy to the patient's atria.
The atrial defibrillator and method of the present invention provide such a warning. The warning is in the form of electrical energy applied to internal tissue of the patient and being of a quantity so as to be discernable by the patient without pain or other undesirable effects. The warning also provides a sufficient time in advance of the delivery of the cardioverting electrical energy to afford the patient with an opportunity to prepare for it. For example, if the patient is standing or walking and receives the warning, the patient may wish to find a place to sit in preparation. As another example, if the patient is driving an automobile and receives the warning, the patient may wish to safely pull off the road and park in preparation. As a result, in providing the warning to the patient, the atria of the patient may be cardioverted with a degree of increased safety not heretofore possible.